1. Field of the Invention
This invention relates to a coform material having improved fluid handling characteristics suitable for use in disposable personal care absorbent articles such as feminine hygiene products. Improved fluid handling is achieved by application of a surfactant treatment system which imparts an enhanced fluid intake rate on multiple insults and a significantly durable hydrophilic character.
2. Description of Prior Art
Absorbent personal care articles such as sanitary napkins, disposable diapers, incontinent-care pads and the like are widely used, and much effort has been made to improve the effectiveness and functionality of these articles. These articles generally include a liquid absorbent material backed by a liquid-impervious barrier sheet. To enhance the sense of comfort, the absorbent material has a facing of a material which masks at least the body-facing surface of the product. This cover material not only contains the absorbent material but also protects the wearer from continuous direct contact with moisture from previously wetted absorbent material. The cover material is typically a relatively low basis weight nonwoven fabric.
The production of nonwoven fabrics has long used meltblown, coform and other techniques to produce webs for use in forming a wide variety of products. Coform nonwoven fabrics are produced by combining separate polymer and additive streams into a single deposition stream in forming the nonwoven webs. Such a process is taught, for example, by U.S. Pat. No. 4,100,324 to Anderson et al. which is hereby incorporated by reference. U.S. Pat. No. 4,818,464 to Lau discloses the introduction of superabsorbent material as well as pulp, cellulose, or staple fibers through a centralized chute in an extrusion die for combination with resin fibers in a nonwoven web. The pulp, staple fibers, or other material are added to vary the characteristics of the resulting web, for example, strength and absorbency.
FIG. 1 is a partially schematic side elevation, partially in section, of a prior art method and apparatus for producing coform nonwoven fabrics. Basically, the method of formation of the coform nonwoven web involves extruding a molten polymeric material through a die head 11 into fine streams and attenuating the streams by converging flows of high velocity, heated gas (usually air) supplied from nozzles 12 and 13 to break the polymer streams into discontinuous microfibers of small diameter. The die head preferably includes at least one straight row of extrusion apertures. In general, the resulting microfibers have an average fiber diameter of up to only about 10 microns with very few, if any, of the microfibers exceeding 10 microns in diameter. The average diameter of the microfibers is usually greater than about one micron, and is preferably within the range of about 2-6 microns, averaging about 5 microns. While the microfibers are predominately discontinuous, they generally have a length exceeding that normally associated with staple fibers.
The primary gas stream 10 is merged with a secondary gas stream 14 containing individualized wood pulp fibers so as to integrate the two different fibrous materials in a single step. The individualized wood pulp fibers typically have a length of about 0.5 to 10 millimeters and a length -2-maximum width ratio of about 10/1:400/1. A typical cross-section has an irregular width of 30 microns and a thickness of 5 microns. The integrated air stream is then directed onto a forming surface to air form the nonwoven fabric. In the configuration shown in FIG. 1, the secondary gas stream 14 is formed by a pulp sheet divellicating apparatus comprising a picker row 20 having picking teeth for divellicating pulp sheets 21 into individual fibers. The pulp sheets 21 are fed radially, that is, along a picker row radius, to the picker row 20 by means of rows 22. As the teeth on the picker row 20 divellicate the pulp sheets 21 into individual fibers, the resulting separated fibers are conveyed downwardly toward the primary air stream through a forming nozzle or duct 23. A housing 24 encloses the picker row 20 and provides a passage 25 between the housing 24 and the picker row surface. Process air is supplied to the picker row in the passage 25 by means of duct 26 in sufficient quantity to serve as a medium for conveying the fibers through the forming duct 23 at a velocity approaching that of the picker teeth. The air may be supplied by any conventional means as, for example, a blower.
To convert the fiber blend in the integrated stream 15 into an integral fibrous mat or web, the stream 15 is passed into the nip of a pair of vacuum rolls 30 and 31 having foraminous surfaces that rotate continuously over a pair of thick vacuum nozzles 32 and 33. As the integrated stream 15 enters the nip of the rolls 30 and 31, the carrying gas is sucked into the two vacuum nozzles 32 and 33 while the fiber blend is supported and slightly compressed by the opposed surfaces of the two rolls 30 and 31. This forms an integrated, self-supporting fibrous web 34 that has sufficient integrity to permit it to be withdrawn from the vacuum roll nip and conveyed to a windup roll 35.
In order to satisfy the requirements for immediate transfer of each liquid application or insult through the cover material of feminine hygiene products as discussed hereinabove, it is necessary that the surfaces of the cover material or the surface of the fibers forming the nonwoven fabrics be first wetted by the liquid. Wettability of nonwoven webs or fibers thereof is known to be achievable by treating the surface thereof with surfactants. See, for example, U.S. Pat. Nos. 4,413,032 to Hartmann et al. and 5,045,387 to Schmalz. Alternative methods of imparting wettability to such materials are taught, for example, by U.S. Pat. No. 5,456,982 to Hansen et al. in which the bicomponent fibers are provided with permanent hydrophilic surface properties by incorporating a surface active agent into the sheath component and optionally by including a hydrophilic polymer or copolymer in the sheath component. See also, U.S. Pat. No. 5,582,904 to Harrington which teaches the incorporation into a polyolefin-containing cast or spin-melt composition for production of nonwoven materials a modifier composition comprising at least one M,M-polyalkoxylate 10-22 carbon fatty acid amine, inclusive of amines having 12-20 carbons and preferably 18 carbon linear straight chain moiety corresponding to that found in stearic or oleic acid, and up to about 60%, including 0.1%-45% by weight of a modifier composition, of a primary or a secondary 10-22 carbon fatty acid amide, such as stearamide.